1. Field of the Invention
The present invention relates to wireless communication, and more particularly, to a wireless communication method of improving frequency efficiency based on a channel function in a wireless communication system and an apparatus thereof.
2. Related Art
A technology of increasing frequency efficiency to transmit data at a high rate basically includes a technology of increasing a modulation level of communication and an MIMO technology of using a multiple antenna. The technology of increasing a modulation level of communication supports 1024 Quadrature Amplitude Modulation (QAM) together with development of a hardware design technology. However, since such a technology requires a high Signal to Noise Ratio (SNR), a transmission distance is restrictive and the technology is sensitive to a channel environment.
Meanwhile, a Multiple Input Multiple Output (MIMO) technology is a technology of increasing frequency efficiency using orthogonality of a spatial channel function. The MIMO technology includes a spatial multiplexing technology which is a technology of linearly increasing a maximum transmission rate proportional to the number of antennas. According to the MIMO technology, if the number of used transceiver antennas and RF transceivers is increased by N times, the frequency efficiency of maximum N times may be increased. However, in this case, since N different signals interfere with other, a high SNR is required. In order know channel information corresponding to each antenna, a complex channel estimation scheme or a complex reception algorithm for obtaining an inverse of a channel matrix is required. Further, in a systematic aspect, since a plurality of Radio Frequency (RF) transceivers and a plurality of antennas are required, power consumption is increased and an installation space is limited. Moreover, since an orthogonal channel function should be created, the MIMO technology is sensitive to characteristics of a real communication channel environment.
In order to solve the above problem, a spatial modulation technology of coding a path of signals transmitted from different antennas may be used. The spatial modulation technology may improve the frequency efficiency by coding an orthogonal channel using a channel function. However, the spatial modulation technology needs a plurality of antenna, and may be implemented by one transceiver based on a single carrier scheme. In order to support a multiple subcarrier based transmission scheme such as Orthogonal Frequency Division Multiplexing (OFDM), since channel coding should be performed by a plurality of sub-carriers, there may be a demand for the same number of RF transceivers by the corresponding number of antennas as in the MIMO technology. In this case, the OFDM is a scheme which carries data in a plurality of orthogonal sub-carriers and multiplexes the sub-carriers to perform wireless communication. In this case, in order to ensure orthogonality between the sub-carriers, the sub-carriers may be arranged on a frequency axis so that an interval between the sub-carriers satisfies Δf=1/Tg. The Tg represents a modulation symbol duration per sub-carrier.
Accordingly, there is a need for a technology of increasing frequency efficiency using a single transceiver.